Consideration about Subsurface Structure of Uemachi Fault Using Geotechnical Borehole Database in Osaka, Japan

摘要

In Osaka, Uemachi Fault is one of the famous active faults. It across the center of Osaka and lies in N–S direction mainly and is more than 40 km in length. Pliocene to Quaternary sediment “Osaka Group” and terrace sediment are found to be deposited in the Osaka Plain. These sediment are very thick layers over 1000m therefore, fault structure are appeared as flexure zone (only vending the strata) and hidden the fault displacement around the surface. In this study, we try to show the flexure zone around central Osaka area using borehole database and decided the site of borehole drilling site and carried out the survey in order to decide the displacement rate of Uemachi fault. Sakuragawa flexure and Suminoe flexure are considered the secondary fault of Uemachi fault system. These are NE-SW trend and only several km lengths. Database show the Sakuragawa flexure wind in the plain. We carried out the drilling the borehole and sampling the core samples in the Sakuragawa flexure zone. The result of compare with the neighbor area, the average displacement speed indicates more active the Sakuragawa flexure rather than Uemachi fault zone.